Electron tube



June 8 1926. A '1,587,786'

J. MAssQLLE E1' AVI.

ELECTRONTUBE :filed April ,4 -1921 F.' I G. 4`.

'35 potential in varying Patented June `8., 1926.

UNITED STATES PATENT OFFICE.-

Josnrrc MASSOLLE, or GRNEWALD, HANS voer, or BERLIN-SCHONEBERG, AND .Tosnr ENGL, or .GBUNEWALTL GERMANY, AssIGNoBS To rar-ERGON .Lml

ZUR/I CH, SWITZERLAND.

ELEo'rnoN rpms...

RUSS

ApplicationA lcd April 4, 1921, Serial N10. 458,635, ,and in Germany December 2, 1919.P

i The invention relates to electron tubes, articularly to thermionio amplifying tubes.

. he'invention aims to improve the 'effectiveness in operation of amplifier tubes, by overi coming an effect, or,action,-in the operation of amplifiers of-common type, which tends to reduce the amplifications secured thereby. ln the operation ofthe well-known (amplifier. having an effective resistance in series with l the plate-filament path of the tube, across the constant source of potential (B battery) lof the tube, variation of input voltage causes a variation in the plate-filament potential difference. With grid potential increasing from negative to less negative the plate current will increase and the potential difference between plate and filament decreases. The operating conditions of the tube now correspond to a different current-voltage curve;

and a comparison of curves plotted for different potentials at the plate will demonstrate that the amplification indicated by the second curve may be less than that indicated by the first curve.

95 The effectiveness of the tube will, of course be improved ifa characteristic curve of desirable steepness be selected, and if such arrangements be provided that the operation will remain substantially on the same curve,

regardless of varying potential differences between plate and filament. The present invention provides means for accomplishing this object, or, generally speaking, for reducing the effect of variations in the plate the amplification, factor of the tube. This is laccomplished by the provision of an auxiliary anode, vor anode screening member, preferably positioned between the plate or working anode and the 40 grid, and connected to the constant potential source of the tube, preferably in such manner that the potential difference between this screening member and the filament is less than that between the plate or working anode of the tube, and the filament.

` In order that the invention may be more clearly understood, attention is hereby called vto the accompanying' drawings, in which Figure 1 is a diagram giving a series of characteristic curves for a usual type of am plifying tube, indicating the relations between grid potentials and plate current for varying plate potentials, the horizontal coordinate of the diagram indicating grid 'voltages and the vertical co-ordinate indicating plate current in milli-amperes, while the numerals at the left hand Side of the curves indicate the plate potentials of the various curves, in. volts;

Fi 2 is a view 'of an electron discharge tube aving an anodescreening member, or auxiliary anode, in accordance with the present invention; and Y.

Fig. 3 is a diagram of current voltage curves for the construction Shown in Fig. 2, the horizontal co-ordinate indicating grid volta es, and the vertical co-ordinate indicating p ate current in milli-amperes.

The curves Shown in Figure 1 represent by way of example the relations between grid potentials and plate current for varying plate potentials, recorded with ordinary amplifier tubes, the right hand `curve corresponding -to 15 volts plate potential and the curves to the left thereof successively 30, 40, 50, 60,75 and 90 volts. Below 40 volts, in this example, the curves become less steep. It will be noted from the figure that at zero grid voltage, for example, a plate current `of about 0.1 milli-ampere, is indicated at 30 volts plate potential, while at 4:0 volts plate potential the plate current is about 0.25 milliamperes. i

It may be stated that one ofthe factors determining the plate current is the` infiuence of the plateacting through the openings of the grid, which may be considered as the passage of lines of force from the plate 4 through the grid. The characteristic curve described will be moved to the left, into the range of negative grid potentials, as the passage of lines of force through the grid increases. This eifect occurs if the plate potential be kept constant and the meshes of the grid are increased in size, or if the meshes are kept the same size andthe potential at the plate is increased. Conversely, ofcourse, the characteristic is shifted to the vright proportionately as the potential at the plate decreases.

To obtain high amplification itis desirable to operate within the range of negative 'potentials' at the grid, as is well-known, a sufficiently negative grid 'meaning a high resistance between filament and. grid and a relatively high plate current. To attain this, the plate voltage must be sufficiently high. In the example Shown in Figure 1 y,the

' filament path of the curves have maximnm steepness at plate voltages of 4() volts `and upwards. I tis, therefore, desirable to operate on curves of 40 volts plate potential and upwards.

It will be noted that inthe operation'of three electrode amplifying tubes o'f usual construction the working resistance outside the tube is connected in series with the platetube and with the constant source (B-battery). If now, we assume, for example, that the grid potential becomes less negative momentarily because of changing conditions in the input circuit of the tube, the internal resistance of the tube between plate and filament then decreases and the plate circuit current increases. The drop of potential across the external resistance increases and the potential drop Within thetube between plate and filament decreases. That is to say, the electrical conditions within the tube no longer correspond to ythe current-voltage curve which represented them before the change in input potential, but to another currentfilament by an external connection whichl voltage curve situated further to the right in a diagram such as that of Figure l, in which case the amplification may not be so good. i

In the construction shown in Fig. 2 i1- lustrating the present invention, the input circuit is connected across the grid g and the filament k as usual, variations in the input circuit causing a varying difference of potential eg across the grid and filament. The plate a2 is shown as connected to the includes the resistance lw and the source of steady plate current indicated as the battery ea. l

The anode screening member a is" shown as connected to the positive pole of battery ea. Resistance w is included in the connection between plate a2 and the positive pole 0f the battery, whereasy this resistance is not included in the connection between the anode screen, or auxiliary plate, a and the positive pole of thebattery. Accordingly, this arrangement provides for a greater drop of potential between the anode screen a and the 'ilament, than exists between plate a' and the filament because o f the drop of the potential through resistance w. The

out-going circuit may be considered as connected across the terminals of resistance "w.'

In the arrangement shown, which is preferred, the anode screen a is located between grid g and plate a2. The potential supplied to anode screen a by the battery or'source ea is as nearly constant as possible. The eliect of this screening or protecting electrode a is to greatly decrease the electrostatic lines of force from the working anodeor plate a2 through the` openings of the grid. By decreasing this flux throu h the grid to a minimum variation in t e partof the electrons than that on the ever, being preferred.

'In the example shown, the varying voltage of plate u has practically no influence on the ran e or position of the current-voltage curve 0% the tube: This is demonstrated by the curves shown in Fig. t which were obtained with a tube constructed `according to the invention. A constant potential of volts was applied to the anode screen or auxiliary anode a whilelvoltagcs of 80 volts respectively were applied to the working anode or plate az. It will be noted that both curves start from the same'point on the horizontal co-ordinate and separate from each other very sli htly in the course of the upward rise of te curves, showing that the varying voltage of the plate, in this arrangement, exerts very little lniluence on the position of the curve. The screening member a grid-like or perforated in form. When this member has small meshes or openings therethrough and there is a relatively large distance between members a and a, a pro- 20 volts and is preferably portionately small number of electrons from i the heated filament c will pass through the member a and reach plate a2. If, however, the meshes or4 the width of the openings in anode screen a are increased, or if the distance between members a and a2 is reduced, the number of electrons passing throu h member a to the plate a becomes relative y greater. As an extreme example, the anode screen a may be reduced to consist of a single wire only, in which case its Ysurface becomes very small in comparison with that of plate a', and in that case a considerable emitted by the cathode willpass to plate a. v

It will' be noted that as shown in the example in Fig. 2, the full potential of battery ea is applied constantly to the anode screen a', while the potential at plate a2 is reduced by the amount of the potential. drop across the resistance '1o. The potential of battery ea may be divided, by means of a potentiometer or otherwise as desired .to roduce other relations than those shown tween the potentials at members a and a', the only essential requirement, for best operation, being the fulfillment of the condition that the potential on plate a2 must be less anode screen a.

between saidl source andA screenin 1. In electron discharge tubes, the combination of a vaeuous tube having plate, grid and filament,. and anode screening means, an input circuit connected to the grid and filament, a source o potential, and connections therefrom to the plate, filament and screening means, including greater resistance between said source and plate than for imposing a greater potential ifi'erence between said screening means and filament than between said plate and filament.

2. In-electron discharge tubes, vthe com bination 'of a vacuous tube having plate,

gridY and filament, and. anode screening means, an input v 'ircu-it connected to the "rid and filament, a ,sourcel of potential, having its ynegative terminal -connected to the filament, a resistance connected in series between the plate 'and' the positive terminal .of

the source, and a connection between said screening means and a point between the positive pole of the source and the resistance.

' 3. In electron discharge tubes, the coinbination of a racuous tubeliaving plate,

grid and filament, and anode screening.

means interposed between the plate and grid output terminals connected to said plate and filament, 'an input circuit connected to the grid and filament` a source of potential, and connections therefrom to said 4output terminals and screening means, in-

cluding an impedance in the connectionto one lof said output' terminals, for imposing agreater potential difference between said screening means and filament than between said plate and filament. l

4. In electron discharge tubes, the combination of a vacuous tube having anode,

cathode 'and control electrode, and anode screening means, means for impressing a means,

varying potential across'the cathode and control electrode, a source of steady potential connected between'the anode and cathode, a

connection between the positive side of said source and said anode screening means, and

means interposed between said source and anode for reducing the potential difference between the anode .and cathode due to said source.

. 5.' In electron discharge tubes. the coin- -bi`nation of a. vacuous tube having anode,

cathode and control electrode, and anode screening means, means for impressing a varving potential across' the cathode and control electrode, said anode screening means bein-g interposed between said .anode and control electrode connections external to the .tube between the anode and cathode,

and means for imposing a potential di'fferencebetvrecu said anode nud cathode and a steady, relatively great, potential difference between said Vanode screening means and said cathode.

6. In electron discharge tubes, the combination of a vacuous tube having anode,

tures.

JOSEPH MASSOLLE. HANS VOGT. Dit. JOSEF ENGL. 

